The present invention relates to communication devices such as digital and analog radio sets for voice and/or data processing, as well as to a method of operating these sets.
In speech communication with (digital or analog) radio sets the volume of the voice signal is decisive for the intelligibility. The speaker can speak aloud or in a low voice and next to or remote from the apparatus. The voice signal generated by the microphone in the transmitter is therefore subject to variations in dynamics. The listener, however, expects to receive a largely uniform volume (low dynamics). Variations of the signal should therefore be suppressed along the transmission path from the microphone to the loudspeaker.
It is common to ensure a compression of the dynamic range of the voice signal by means of closed-loop control circuits which are connected in the transmitter between the microphone and the modulator. Closed-loop control circuits, however, present disadvantages which become manifest in recovery time constants, noise and increased nonlinear distortion factors of the voice signal. Low-pass filters for attenuating the harmonics introduced as parasitic effects by the closed-loop control circuit may possibly produce an undesirable effect on the voice signal.
An alternative dynamic compressor is composed of a first transponder, a band-pass filter, a second transponder and a common oscillator. On account of the higher manufacturing costs and dimensions (e.g. silicon area), however, this compressor does not appear to be attractive for application in a radio apparatus.
The problem underlying the invention consists in the provision of an improved communication device which mitigates or avoids the aforementioned disadvantages and these and other disadvantages and limitations of the prior art. This problem is solved with a device of the claimed general type and with a method in accordance with the claims.